title: Alterations in differentiation and apoptosis induced by bufalin in cJun overexpressing U-937 cells.
abstract: Recent evidence suggests that c-jun plays a pivotal role in macrophage differentiation induced by multiple agents and that cJun overexpression induces partial macrophage differentiation in the leukemic cell line U-937. The novel differentiating agent bufalin, a Na+/K+ ATPase inhibitor, has also been shown to induce macrophage differentiation in U-937. In order to further define the role of c-jun in macrophage differentiation, we examined the function of c-jun/AP-1 during bufalin induced differentiation in both c-jun transfected and parental U-937 cells. In contrast to phorbol esters, bufalin does not significantly stimulate c-jun or c-fos mRNA expression or AP-1 transactivation. However, bufalin treatment leads to markedly greater morphologic and functional changes indicative of more extensive differentiation in the cJun overexpressing cells compared to the non-transfected controls. Furthermore, cJun overexpressing cells maintain greater viability in the presence of bufalin and arrest in a different phase of the cell cycle than do control cell lines (G0/G1 versus S/G2M, respectively), although some apoptosis occurs in all cell lines treated with bufalin. These data suggest that while bufalin can induce some degree of differentiation in U-937 cells independent of c-jun/AP-1 controlled pathways, the involvement of these pathways by enforced cJun expression enhances the extent of differentiation and shifts the balance between differentiation and apoptosis.
authors.affiliation: Medicine Branch, Division of Clinical Sciences, National Cancer Institute, 9610 Medical Center Drive, Room 300, Rockville, MD 20850, USA.
authors.forename: E
authors.initials: E
authors.lastname: Szabo
authors.forename: J
authors.initials: J
authors.lastname: Francis
authors.forename: M J
authors.initials: MJ
authors.lastname: Birrer
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015152:Blotting, Northern; D002018:Bufanolides / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects*; D004587:Electrophoresis, Agar Gel; D005434:Flow Cytometry; D006801:Humans; D008264:Macrophages / Q000166:cytology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014162:Transfection; D020298:U937 Cells / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D002018:Bufanolides; D016760:Proto-Oncogene Proteins c-fos; D018808:Transcription Factor AP-1; D000254:Sodium-Potassium-Exchanging ATPase; C022777:bufalin